Abstract:

A heating/cooling system has improved operating efficiencies due to low
superheat provisions and a specially configured compressor oil return.
For certain systems, such as direct exchange geothermal heating/cooling
applications having sub-surface heat exchanges extending at least 100
feet below the surface and using R-410A refrigerant, a specific
compressor oil may be used to further improve efficiency.

Claims:

1. A heating/cooling system, comprising:an exterior heat exchanger;a
compressor;an oil separator;heating and cooling mode expansion devices;an
interior heat exchanger;an accumulator for holding liquid refrigerant,
the liquid refrigerant defining a liquid refrigerant level within the
accumulator;a suction vapor line having a lower distal end disposed
within the accumulator, the accumulator suction vapor line including at
least one discharge hole situated below the liquid refrigerant level;
anda compressor suction line having a first end in fluid communication
with an interior of the accumulator and a second end in fluid
communication with an interior of the compressor.

2. The system of claim 1, in which the suction vapor line lower distal end
comprises an open end.

3. The system of claim 2, in which the suction vapor line includes no
holes other than the open end.

4. The system of claim 1, further comprising a filter operably coupled to
the compressor suction line first end, the filter being configured to
prevent passage of liquid refrigerant.

5. The system of claim 1, further comprising an oil return line having a
first end in fluid communication with an interior of the oil separator
and a second end in fluid communication with the compressor suction line.

6. The system of claim 5, in which the oil separator is configured to be
at least 98% efficient.

7. The system of claim 5, further comprising a coalescing filter disposed
in the oil separator.

8. The system of claim 8, in which the coalescing filter is configured to
be at least 99% efficient and to filter down to at least 0.3 microns.

9. The system of claim 5, in which the compressor suction line includes a
U-bend disposed below the liquid refrigerant level in the accumulator,
and a vapor bleed port is formed in a portion of the compressor suction
line disposed within the accumulator and above the liquid refrigerant
level.

10. The system of claim 9, in which the vapor bleed port has a diameter of
approximately 0.025 to approximately 0.03 inches per ton of system design
capacity.

11. The system of claim 5, in which the compressor suction line includes a
U-bend disposed below the liquid refrigerant level in the accumulator,
and in which an oil return orifice is formed at a base of the U-bend.

12. The system of claim 11, in which the oil return orifice has a diameter
of approximately 0.02 to approximately 0.0396 inches for a compressor
capacity of approximately 2 to 5 tons.

13. The system of claim 1, in which the exterior heat exchanger comprises
a geothermal, sub-surface heat exchanger.

14. The system of claim 13, in which the geothermal, sub-surface heat
exchanger extends to a depth of at least 100 feet, and in which the
system uses an R-410A refrigerant.

15. The system of claim 14, further comprising a compressor lubricating
oil rated for use in temperatures exceeding 200 degrees F.

16. The system of claim 15, in which the compressor lubricating oil
comprises a Hatco 32 BCE lubricating oil.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001]The present application claims the benefit of U.S. Provisional
Application Ser. No. 60/986,707, filed on Nov. 9, 2007, the entirety of
which is incorporated herein by reference.

[0003]Geothermal ground source/water source heat exchange systems
typically include closed loops of tubing that are buried in the ground,
or submerged in a body of water. Fluid is circulated through the loops of
tubing so that the fluid either absorbs heat from or rejects heat into
the naturally occurring geothermal mass and/or water surrounding the
tubing. The ends of the tubing loop extend to the surface and are fluidly
coupled to an interior air heat exchanger. The naturally warmed or cooled
fluid is circulated through the interior air heat exchanger to warm or
cool an interior space.

[0004]Common and older geothermal water-source heating/cooling systems
typically have a pump for circulating a fluid comprised of water, or
water with anti-freeze, in plastic (typically polyethylene) underground
geothermal tubing so as to transfer geothermal heat to or from the ground
in a first heat exchange step. In a second heat exchange step, a
refrigerant heat pump system transfers heat to or from the water.
Finally, in a third heat exchange step, an interior air handler
(comprised of finned tubing and a fan) transfers heat to or from the
refrigerant to heat or cool interior air space.

[0005]Newer design geothermal DX heat exchange systems have only two heat
exchange steps. DX systems typically have refrigerant fluid transport
lines placed directly in the sub-surface ground and/or water. The
sub-surface refrigerant lines are typically comprised of copper tubing. A
refrigerant fluid, such as R-22, or the like, is circulated through the
lines to transfer geothermal heat to or from the sub-surface elements in
a first heat exchange step. DX systems only require a second heat
exchange step to transfer heat to or from the interior air space,
typically by means of an interior air handler. Consequently, DX systems
use fewer heat exchange steps and do not require power to run a water
pump, and therefore are generally more efficient than water-source
systems. Further, since copper is a better heat conductor than most
plastics, and since the refrigerant fluid circulating within the copper
tubing of a DX system generally has a greater temperature differential
with the surrounding ground than the water circulated through the plastic
tubing of a water-source system, generally, less excavation and drilling
is required, thereby decreasing installation costs.

[0006]While most in-ground/in-water DX heat exchange designs are feasible,
various improvements have been developed to enhance overall system
operational efficiencies. Several such design improvements, particularly
in direct expansion/direct exchange geothermal beat pump systems, are
taught in U.S. Pat. No. 5,623,986 to Wiggs; U.S. Pat. No. 5,816,314 to
Wiggs, et al.; U.S. Patent No. 5,946,928 to Wiggs; and U.S. Pat. No.
6,615,601 B1 to Wiggs, the disclosures of which are incorporated herein
by reference. Such disclosures encompass both horizontally and vertically
oriented sub-surface heat geothermal heat exchange means.

[0007]Conventional DX system typically heat or cool at least one control
medium. A control medium could be, for example, water, water and/or
antifreeze, a solid (such as concrete), or a vapor (such as air in an
interior room). In a conventional DX system design, the control medium is
air in an interior space, and the sub-surface geothermal heat exchange
tubing provides heat to the interior air by means of an interior
air-handler. In a conventional DX system design, the system is used to
either heat or cool, but is not designed to simultaneously heat and cool
different control media or similar control media located in different
interior spaces.

[0008]It is advantageous to maintain or increase the operational
efficiencies of a DX system. The subject matter disclosed herein
primarily relates to various improvements that will maintain or increase
system operational efficiencies

SUMMARY OF THE DISCLOSURE

[0009]The exemplary DX systems disclosed herein advantageously maintain or
increase system operational efficiencies by providing an optimum
superheat level; providing mostly refrigerant vapor to the compressor;
and providing a preferred compressor lubricating oil and oil return means
for a DX system using an R-410A refrigerant, particularly when the
sub-surface geothermal heat exchange tubing of the DX system is installed
in deep wells, exceeding 100 feet in depth.

[0010]Maintaining a very low superheat, but at a temperature above a zero
superheat, may increase system operational efficiencies. If the superheat
is too low, being very near to or at the refrigerant saturation level
and/or very near to or at zero degrees F, as taught in U.S. Pat. No.
6,058,719 to Cochran, two problems are encountered. First, ice very
quickly builds up on any un-insulated portion of the suction line within
the compressor box (particularly in the heating mode, since vaporizing
liquid within the suction refrigerant transport lines traveling to the
compressor removes heat from the lines and the cold lines freeze
condensing moisture coming from the air), thereby increasing concerns
with water, mold, and mildew buildup as the ice periodically melts.
Second, at or slightly below zero superheat, some liquid phase
refrigerant is necessarily pulled into the system's compressor, which
compressor attains maximum efficiencies via compressing only vapor state
refrigerant.

[0011]The '719 patent achieves near (slightly below, of necessity, as
hereinafter explained so as to effect oil return), or at, zero superheat
conditions by means of thoroughly mixing liquid phase refrigerant in a
refrigerant storage container with incoming refrigerant fluid (mostly
vapor) from the heat exchanger utilized. The resulting thorough mixture
of saturated refrigerant vapor and refrigerant liquid pulled into the
compressor does have enough liquid form refrigerant to carry refrigerant
oil back to the compressor, after the oil has circulated throughout
Cochran's entire system in conjunction with the refrigerant. However,
again, liquid phase refrigerant impairs the operational efficiency of the
compressor, and may excessively dilute the lubricating oil within the
compressor itself via flow through of too much liquid phase refrigerant,
thereby shortening compressor life. Cochran's design, therefore, must
supply saturated refrigerant vapor (which is present at zero degrees
superheat) to the compressor, as he has neither indicated nor shown nor
described any other compressor lubricant oil return means. Since oil can
be carried back into the compressor via tiny liquid refrigerant
molecules/droplets, or the like, (which liquid phase molecules/droplets
exit at saturation, or lesser, temperatures) Cochran must return
saturated refrigerant, containing at least some liquid phase refrigerant,
back to the compressor, or his compressor would eventually burn out.

[0012]In conventional heat pump systems, the compressor lubricating oil
mixes with the vapor refrigerant as well as the liquid phase refrigerant
in the bottom of standard accumulators. The oil that has mixed with the
liquid phase refrigerant is typically pulled back into (and returned to)
the compressor by means of a small orifice in the bottom of a suction
line U-tube disposed within the accumulator (the top of the U tube within
the accumulator primarily limits the refrigerant being pulled into the
compressor to one of a mostly vapor state). The orifice size for oil
return at the bottom of the U bend suction line within the accumulator,
in most conventional two to five ton compressors, for example, is about
0.04 inches to 0.055 inches in diameter (diameter orifices are
proportionately larger for larger compressor sizes).

[0013]However, in addition to providing a means to return oil to the
compressor in conventional systems, some liquid phase refrigerant is also
pulled into the compressor. While the amount of liquid phase refrigerant
pulled into the compressor is relatively small, and therefore the
compressor is normally not "slugged" or otherwise materially damaged, the
presence of liquid phase refrigerant may impair compressor operational
efficiencies. Further, so as to intentionally avoid slugging compressors,
compressor manufacturers typically call for the maintenance of 15 degrees
to 25 degrees superheat. While this superheat level helps protect the
compressor from being slugged (slugging occurs via suctioning too much
liquid phase refrigerant through the compressor, which is designed to
compress vapor and not liquid), it may impair the operational
efficiencies of the heating/cooling system, which are maximized at a
point as close as possible to, but still above, zero degrees superheat,
so long as not too much liquid phase refrigerant enters the compressor.
Through testing, applicant has found that keeping superheat levels
between 0.5 and 10 degrees provides optimum operational efficiencies in a
DX system.

[0014]Cochran further uses eight holes, which are about 0.077 inches in
diameter, in approximately 4 to 5 ton system designs for example, to
achieve at or slightly below zero superheat refrigerant saturation level
in the suction line to the compressor, and to return oil to the
compressor. Consequently, Cochran's system introduces increased levels of
liquid phase refrigerant back into the compressor, to an even greater
extent than other conventional heat pump system designs, such as
air-source heat pump system designs for example. While Cochran teaches
the use of a deflector shield to help prevent excessive amounts of liquid
from being pulled into the compressor, it still introduces more liquid
phase refrigerant into the compressor than other conventional designs,
which, as previously explained, can impair system operational
efficiencies and/or can shorten compressor life.

[0015]A preferable objective would be to maintain a very low superheat
level, preferably between 0.5 degrees F. and 10 degrees F., in the
suction line to the compressor, so as to maintain low compressor
operating temperatures, thereby extending compressor life and reducing
operational power requirements. The above is achieved while minimizing
the amount of liquid phase refrigerant required to be returned to the
compressor itself and providing adequate return of lubricating oil to the
compressor.

[0016]Extensive testing has demonstrated that this objective is
accomplished by means of adjusting the desired amount of return
refrigerant vapor released into the accumulator, at adjustment points
above and below the liquid phase refrigerant within the system's
accumulator, by providing moderately sized holes within the wall of the
return vapor refrigerant transport line within the accumulator, at
selected and preferred locations, within the accumulator itself.

[0017]Testing has shown that to decrease or lower superheat, one should
decrease the number and/or size of the upper holes within the suction
refrigerant supply line, which are situated above the liquid state
refrigerant within the within the accumulator, and increase the number
and/or size of lower holes within the suction refrigerant supply line,
which are situated below the liquid state refrigerant within the
accumulator. The total number and area size of holes/ports, both above
and below the liquid phase refrigerant within the bottom portion of the
accumulator, may be equal the total area size of the interior open distal
end of the suction refrigerant supply line within the accumulator, which
interior open distal end of the suction refrigerant supply line would be
sealed shut when holes are provided in the side of the suction
refrigerant supply line within the accumulator.

[0018]Testing has shown that to increase or raise superheat, one should
increase the number and/or size of upper holes within the suction
refrigerant supply line, which are situated above the liquid state
refrigerant within the within the accumulator, and decrease the number
and/or size of lower holes within the suction refrigerant supply line,
which situated below the liquid state refrigerant within the accumulator.
The total number and area size of holes/ports, both above and below the
liquid phase refrigerant within the bottom portion of the accumulator,
may be equal the total area size of the interior open distal end of the
suction refrigerant supply line within the accumulator, which interior
open distal end of the suction refrigerant supply line would be sealed
shut when holes are provided in the side of the suction refrigerant
supply line within the accumulator.

[0019]Further, testing has indicated the best design, so as to operate
within a preferable low superheat temperature range, above zero but less
than 10 degrees, is to leave the lower bottom distal end of the suction
refrigerant supply line, which supply line is within the accumulator and
is positioned below the liquid state refrigerant, completely open, so
that there is only one hole below the liquid phase refrigerant level, and
so that there are no holes above the liquid level within the accumulator.
Testing has shown that the refrigerant vapor bubbles exiting the open
lower distal end of the suction refrigerant supply line to, and within,
the accumulator, when positioned below the liquid phase refrigerant level
within the accumulator, are large enough so as not to effect full
saturation of the refrigerant entering the suction line to the
compressor. However, the vapor refrigerant bubbles are of adequate size
to mix with the liquid refrigerant within the bottom portion of the
accumulator so as to maintain operational superheat levels between 0.5
degrees F. and 10 degrees F.

[0020]Simultaneously, at such low superheat levels, testing has
demonstrated that the amount of liquid phase refrigerant entering the
compressor may be minimized by installing a liquid refrigerant filter at
or near the intake point of the suction line to the compressor within the
accumulator. The liquid refrigerant filter may be of any type that is
non-corrosive to refrigerant transport tubing, and that is non-corrosive
to steel and other refrigeration parts/equipment/fittings, so long as the
filter prevents one of all and mostly all liquid phase refrigerant from
flowing through, and solely permits one of all and mostly all vapor phase
refrigerant flow.

[0021]Additionally, an oil separator may be used with an oil filter that
preferably removes about 99%, or more, of the oil from the compressor, so
as to minimize the amount of oil that is entrained within the liquid at
the bottom of the accumulator. For example, the filter may be a
coalescent oil filter is capable of filtering to at least 0.3 microns and
is at least 99% efficient. The oil separator may also have a sight glass
to facilitate viewing of the oil level. An oil separator typically has a
hinged float that opens up an oil return line to one of the compressor
and the suction line to the accumulator when the oil level gets too high.
Preferably, the oil is returned to a point at the suction line to the
compressor, but after the suction line has exited the accumulator.

[0022]Alternatively, a helical oil separator that is at least 98%
efficient may be used to return oil, with the helical oil separator and
the oil return line positioned as herein described for an oil separator
with a highly efficient filter.

[0023]In a system using an accumulator for traditional purposes, the hot
oil from an oil separator may be returned to the suction line leading to
the accumulator, so as to help vaporize any unwanted liquid refrigerant
in the accumulator. However, in the subject design taught herein, it is
desirable to maintain a cool liquid refrigerant in the bottom portion of
the accumulator so as to help maintain a low suction line superheat to
the compressor. Consequently, in the subject design taught herein, the
oil is returned directly to the compressor suction line, thereby
by-passing the accumulator.

[0024]As an additional advantage, the use of such an efficient oil
separator that by-passes the accumulator allows only minute amounts of
oil to travel into the general refrigerant transport line circuitry. This
provides a heat transfer advantage in the sub-surface geothermal heat
exchanger and in the interior heat exchanger, as the interior walls of
the refrigerant transport tubing are not coated with as much oil as in a
conventional system and heat transfer is thereby improved (an oil coating
on the walls of heat transfer tubing inhibits heat transfer and reduces
optimum efficiencies).

[0025]Still another advantage provided, via the use of such an efficient
oil separator that by-passes the accumulator, is that the oil return
orifice in the bottom of the suction line U bend within a traditional
accumulator may now be much smaller (such as by at least 72%) than the
traditional aforesaid 0.04 inch to 0.055 inch diameter for a 2-5 ton
system compressor, because materially less oil now needs to be returned
via this orifice. This also means at least 28% less liquid refrigerant is
now required to be pulled into the suction line to the compressor,
thereby increasing compressor operational efficiencies. Thus, such a
preferable 72% smaller oil return orifice would preferably have a 0.02
inch to a 0.0396 inch diameter.

[0026]However, when such a conventional/traditional accumulator is used,
in conjunction with one or more of the subject disclosures as taught
herein, a vapor bleed port hole may be provided near the top of the
portion of the U bend that exits directly to the compressor, which vapor
bleed port hole may be positioned above the liquid refrigerant level
within the accumulator. The subject vapor bleed port hole prevents
excessive liquid slugging within the compressor upon system start-up,
which excessive slugging could otherwise be caused via liquid phase
refrigerant that may have completely filled the lower portion of the U
bend via the oil return orifice hole in the bottom of the U bend during
system inoperative periods. The subject vapor bleed port hole, when used
in conjunction with one or more of the disclosures taught herein, may
have between a 0.025 inch and a 0.03 inch diameter size per ton of system
design capacity. One ton equals 12,000 BTUs, and system design
capacities, in tons, are typically calculated via ACCA Manual J, or the
like, and are well understood by those skilled in the art.

[0027]Additionally, when such a conventional accumulator is used, in
conjunction with one or more of the subject disclosures as taught herein,
it would be advantageous, although not mandatory, to install a liquid
refrigerant filter at the top of the suction refrigerant line (the intake
to the U bend) within the accumulator that supplies the compressor. Such
a filter is preferable in that it will help to safeguard against any
excessive liquid phase refrigerant possibly getting into the compressor,
as a result of system overcharging, or the like. However, under normal
conditions, so long as the top of the suction line is safely above the
liquid level within the accumulator, such a filter is not mandatory.

[0028]Rather than a conventional accumulator with an interior U bend
suction line to the compressor, however, a specially designed accumulator
may be used in conjunction with one or more of the subject disclosures as
taught herein. Such a specially designed accumulator would have a
refrigerant suction line having at least one upper hole above the liquid
refrigerant level within the accumulator, and with at least one lower
hole below the liquid refrigerant level within the accumulator. A
refrigerant liquid filter would preferably be positioned near the top of
the accumulator (above the liquid refrigerant level), with the liquid
filter being directly attached to the entry segment of the suction line
traveling to the compressor. Additionally, instead of a small orifice in
the bottom of a U bend in the suction line within the accumulator (as
would be provided in a conventional accumulator with an interior U bend),
a small oil return line would preferably be extended from below the
liquid refrigerant level within the accumulator to a segment of the
actual direct suction line to the compressor, thereby totally by-passing
the refrigerant liquid filter within the accumulator.

[0029]Testing has shown that the systems disclosed herein may be optimized
when it is charged with an R-410A refrigerant, and when a scroll
compressor is used, in lieu of more common reciprocal compressors. A
special lubricating oil may be used with the scroll compressor, and is
particularly advantageous when the system has liquid and vapor
refrigerant transport tubing extending to depths in excess of 100 feet
below the surface. In such deep well applications, depending on varying
miscellaneous conditions, compressor hot gas discharge temperatures can
periodically exceed 200 degrees F. For example, a standard compressor
lubricating oil recommended by Emerson Climate Technologies, Inc., with a
USA office at 1675 West Campbell Road, Sidney, Ohio 45365, which company
manufactures Copeland Scroll Compressors, is Copeland Ultra 32-3MAF
Polyol Ester Oil, Synthetic Refrigeration Oil, Part No. 998-E022-01.
However, such oil, or the like, is fine so long as system operating
temperatures remain below about 190 degrees F., but such oil can become
impaired if compressor discharge temperatures exceed 200 degrees F.
Therefore, for use in conjunction with the subject system designs as
disclosed herein, and particularly for use in conjunction with a DX
system deep well application (in excess of 100 feet deep), in conjunction
with a scroll compressor operating on an R-410A refrigerant, a Hatco 32
BCE lubricating oil, or the like, should preferably be utilized, as it
can withstand system operating temperatures in excess of 220 degrees F.
(as can be periodically produced by the unique designs and conditions
disclosed herein) without impairment, which is preferable in the
applications and conditions herein described. Hatco 32 BCE lubricating
oil is manufactured by the Hatco Corporation, a Chemtura Company, of 1020
King Georges Post Road, Fords, N.J. 08863.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]For a more complete understanding of the disclosed methods and
apparatus, reference should be made to the embodiments illustrated in
greater detail on the accompanying drawings, wherein;

[0031]FIG. 1 is a schematic side elevation view of a DX system constructed
according to the teachings of the present disclosure; and

[0032]FIG. 2 is an enlarged, schematic side elevation view of an
alternative embodiment of an accumulator for use in a DX system.

[0033]It should be understood that the drawings are not necessarily to
scale and the disclosed embodiments are sometimes illustrated
diagrammatically in partial views. In certain instances, details which
are not necessary for an understanding of the disclosed methods and
apparatus, or which render other details difficult to perceive, may have
been omitted. It should be understood, of course, that this disclosure is
not limited to the particular embodiments illustrated herein.

DETAILED DESCRIPTION

[0034]The following detailed description is of the best presently
contemplated mode of carrying out the subject matter disclosed herein,
The description is not intended in a limiting sense, and is made solely
for the purpose of illustrating the general principles of this subject
matter. The various features and advantages of the present disclosure may
be more readily understood with reference to the following detailed
description taken in conjunction with the accompanying drawings.

[0035]FIG. 1 shows a DX heat pump system 50 that includes a compressor 1,
an oil separator 3, a reversing valve 4, vapor refrigerant line 5, liquid
refrigerant line 6, an optional receiver 10, and an accumulator 17. The
general construction and function of these components are well understood
by those skilled in the art and therefore are not shown or described in
detail herein. The optional receiver 10 is illustrated in FIG. 1 in a
cooling mode, where the refrigerant fluid exits at a base 14 of the
receiver. The directional travel of the refrigerant fluid in the cooling
mode is indicated by arrows 2.

[0036]The refrigerant fluid next flows to a self-adjusting cooling mode
expansion device 23 and finned tubing 24 of an interior air handler. The
finned tubing 24 may be disposed within an enclosure (not shown). A fan
25 may be positioned to blow interior air over the finned tubing 24.
Heated or cooled refrigerant fluid passes through the finned tubing 24 to
transfer heat with the interior air.

[0037]The refrigerant fluid next flows through a reversing valve 4 and
then into the accumulator 17. Here, the accumulator 17 is of a unique
design, as taught herein. A refrigerant suction line 16 to the
accumulator 17 is shown as extending down below a liquid refrigerant
level 30 within the accumulator 17. Further, the refrigerant suction line
16 to the accumulator 17, as it extends within the accumulator 17, has
moderately sized upper holes 21 drilled in its walls above the liquid
state refrigerant level 30, and has moderately sized lower holes 22
drilled in its walls above the liquid state refrigerant level 30, so as
to be able to adjust the superheat to a temperature of between one-half
degrees F. and ten degrees F. The superheat can be increased by drilling
more upper holes 21 and fewer lower holes 22, and the superheat can be
decreased by drilling additional lower holes 22 and fewer upper holes 21
within the refrigerant suction line 16.

[0038]The refrigerant fluid next passes through a refrigerant liquid
filter 20 that prevents one of all and mostly all liquid refrigerant from
entering a segment 29 of the refrigerant suction line extending from the
accumulator 17 to the compressor 1.

[0039]The refrigerant fluid (now entirely, or nearly entirely, vapor) next
flows into the compressor 1, where the vapor is compressed, raising its
pressure and temperature. The hot gas refrigerant then travels into the
oil separator 3, first entering through an oil filter 11 that is
preferably a coalescent oil filter 11 capable of filtering to at least
0.3 microns, and that is at least 98%, and preferably 99%, efficient. An
oil level 13 inside the separator 3 is maintained at a point beneath a
base 14 of the oil filter 11, and the oil level 13 is monitored and
easily checked by means of a sight glass 12. The oil may be returned to
the compressor by means of an oil return line 15.

[0040]The oil return line 15 preferably enters the suction line segment 29
to the compressor 1 at an oil return point 27 disposed downstream of the
accumulator 17, so that hot return oil does not affect (diminish) the
liquid refrigerant level 30 within the accumulator 17, which is used to
maintain a low superheat.

[0041]While primary oil return to the compressor 1 is achieved by means of
the oil separator 3, the oil filter 11, and the oil return line 15 to the
segment 29 of the suction line to the compressor 1, some minor amount of
oil escapes the oil filter 11 (which is not 100% efficient) and mixes
with the refrigerant circulating within the overall system. This oil is
retrieved by means of a small orifice 19 at the bottom of a U-tube
suction line 18 to the compressor 1 within the accumulator 17. Since the
refrigerant liquid filter 20 inhibits oil return as well as liquid
refrigerant, some small portion of liquid refrigerant and oil will be
pulled into the compressor 1 by means of the small orifice 19. However,
since most of the oil is returned via the oil separator 3 and its oil
return line 15 that by-passes the accumulator 17, the orifice 19 size
should preferably be decreased by at least 72% from the conventional 0.04
inch to 0.055 inch interior diameter commonly utilized for two to five
ton system size design compressors 1. The orifice 19 size should be
proportionately increased for larger sized compressors 1. One ton equals
12,000 BTUs, as is well understood by those skilled in the art.

[0042]When a U-tube suction line 18 is used within the accumulator 17,
during non-operative system periods, the liquid refrigerant level 30
within the accumulator 17 can fill the lower segment of the U-tube 18.
Thus, upon system start-up, it is preferable to have a bleed port hole 31
in the upper portion of the side of the U bend 18 that leads directly to
the compressor 1, so as to avoid slugging the compressor 1 during system
start-up. The preferable size of the bleed port hole 31 is between a
0.025 inch and a 0.03 inch diameter size per ton of system design
capacity

[0043]The refrigerant fluid, after exiting the oil separator 3, next
passes through the reversing valve 4 and enters the sub-surface
geothermal heat transfer tubing 5 and 6 within the well/borehole 8, so as
to be able to effect geothermal heat exchange from relatively stable and
naturally occurring temperatures beneath the ground surface 7.

[0044]The geothermal heat transfer tubing 5 and 6 is herein shown as being
comprised of a larger size vapor refrigerant transport line/tube 5
coupled via a refrigerant tube coupling 26 to a smaller size liquid
refrigerant transport line 6 near the bottom of the well/borehole 8 (not
drawn to scale). However, geothermal heat transfer tubing, shown here as
5 and 6, situated below the ground surface 7, can be of a variety of
differing designs, as is well understood by those skilled in the art.

[0045]The refrigerant fluid exiting the well/borehole 8 next travels
through the heating mode expansion device 9, which is inoperative in the
cooling mode (as is well understood by those skilled in the art), and
into the optional receiver 10. The refrigerant flow from a base 14 of the
receiver 10 in the cooling mode, passed a cooling mode expansion device
23, and into the interior heat exchanger. The refrigerant flow path
described above is then repeated.

[0046]FIG. 2 shows an alternative embodiment of an accumulator 17' for use
in a DX system. A refrigerant suction line 16' extends into the
accumulator 17'. The refrigerant suction line 16', however, has no upper
or lower holes in its sidewall (i.e., holes 21 and 22 in FIG. 1), as in
the previous embodiment. Instead, the refrigerant suction line 16'
includes an open distal end 32 disposed below the refrigerant level 30
through which the mostly refrigerant vapor exits.

[0047]A refrigerant liquid filter 20' is positioned near the top of the
accumulator 17' and directly attached to a segment 29' of the suction
line traveling to the compressor (not shown herein). Additionally,
instead of a small orifice (19 in FIG. 1) in the bottom of a U bend (18
in FIG. 1), a small oil return line 15' is shown as extending from below
the liquid refrigerant level 30 to the segment 29' of the suction line to
the compressor, thereby totally by-passing the refrigerant liquid filter
20' which may otherwise inhibit oil return along with its intended
inhibition of liquid phase refrigerant return.

[0048]The foregoing embodiments have been illustrated and described in the
context of a geothermal, direct exchange heating/cooling system. It will
be appreciated, however, that the improvements described herein may
similarly be employed in any other type of heat pump system, including
water- and air-source heat pumps.

[0049]While only certain embodiments have been set forth, alternatives and
modifications will be apparent from the above description to those
skilled in the art. These and other alternatives are considered
equivalents and within the scope of this disclosure and the appended
claims.